Trauma is the leading cause of death for people aged 1-44 year(s) in the United States. The standard of care for injured patients is to control bleeding and volume resuscitation. The goal of resuscitation is to restore tissue perfusion and to correct the imbalance between oxygen supply and tissue oxygen demand. Oxygen delivery must often be increased substantially above normal levels in order to resolve accrued tissue oxygen debt from the period of shock. Currently, resuscitation is guided by systemic indicators such as blood pressure, urine output, and heart rate. After these parameters are normalized up to 85% of patients are still in compensated shock and still have tissue acidosis. The compensated shock state can lead to multiple organ dysfunction syndrome (MODS) which is the leading cause of death in surgical intensive care units. Tissue perfusion or acidosis and oxygen consumption are better criteria to guide adequacy of resuscitation and to predict the development of MODS. The intestine has been demonstrated to be the organ most sensitive to hemorrhagic shock, and it is therefore the ideal target for monitoring. The focus of this work is to develop and test a miniatur photonics-based intestinal perfusion and oxygenation monitoring system specifically optimized for use on the intestine to more accurately guide resuscitation from trauma and hemorrhagic shock. Such a system would help assure the physician that patients are fully resuscitated from shock but without complications of over-resuscitation. Our team will develop and test a novel 3-wavelength implantable photonic system that measures arterial oxygen saturation, venous oxygen saturation, and tissue perfusion using a combination of pulse oximetry and visible (VIS) spectroscopy. The implantable sensor unit will be integrated with electronics for amplifying and processing the signal to minimize noise and a telemetry system to send the signal wirelessly to the bed-side unit. The bed-side unit will be able to process the collected data and display the patient perfusion and oxygenation information in a form that the physician can use to make clinical decisions. The sensor performance will be tested in vitro using novel polydimethylsiloxane (PDMS) based phantoms and in vivo in a rabbit model.